Coevolutionary dynamics and geographic mosaics in the Social Parasite Harpagoxenus sublaevisand its two Host Species

GENERAL INTRODUCTION " Nothing in biology makes sense except in the light of evolution, "-Theodosius Dobzhansky, 1973 The natural history of parasitism has been an immensely fascinating topic for evolutionary biologists in the last couple of centuries. Parasitism represents the most common lifestyle on earth (Thompson 1994), and can be found in all modes of life in the animal kingdom, from simple plathelminthes to vertebrates such as fish and birds (Anderson and May 1982). Moreover, according to most estimates, more than 50% of all known species are parasitic at certain stages of their life cycle (Price 1980). Because of the close relationship between host and parasite, interactions between both organisms are important and have ultimately shaped the organisation of communities and influenced the diversification of life (Thompson 1999b). In all cases, this relationship is asymmetric, because the parasite lives at the expense of its host, causing a fitness reduction in the host and sometimes even its death. Because of its serious implications, the processes and dynamics of this interaction has been studied theoretically and empirically in many scientific sectors The two most important challenges for a parasite are transferring itself or its progeny from one host to another (transmission) and overcoming the defenses of its host (Futuyama 1998). Thus, it is not surprising that there is a strong association between parasite transmission and virulence (Anderson and May 1982; Dunn and Smith 2001). Some parasites are transmitted vertically, e.g. from a host parent to her offspring. However, most parasites are transmitted horizontally among host individuals in a population through the external environment, vectors or contact between hosts. In general, parasitism has to be differentiated from mutualism, commensalism, parasitoid-host and predator-prey interactions as parasites increase their fitness while lowering the fitness of its host drastically which leads however not involuntary to host´s death. In mutualisms, both interactants derive a fitness benefit from their relationship. Commensalism describes a symbiotic relationship between two organisms, where one benefits and the other is not significantly harmed, while parasitoids live part of their life on or GENERAL INTRODUCTION 2 within a single host organism, which they ultimately kill. Finally predators feed on another living organism. Evolution of e.g. life history traits in hosts is often driven by selection exerted through of parasites can be distinguished: Micro-parasites such as viruses, bacteria and fungi exploit the physiology of multicellular hosts that are phylogenetically distant with radically different life histories. …